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The more flame retardants a pregnant woman is exposed to, the greater the chances her child will have lower intelligence. A new paper in the journal Environmental Health Perspectivescalculated that every tenfold increase in exposure to chemicals called polybrominated diphenyl ethers (PBDEs) was linked to a 3.7 point decline in IQ test scores in children. This potential effect is significant. By comparison, a tenfold increase in prenatal exposure to lead—a notorious neurotoxin—is associated with a 7 point decline in intelligence scores in children.

The new study is a meta-analysis summarizing and evaluating all of the relevant research on the safety of these chemicals. The researchers included 10 studies that show a link between flame retardants and intelligence, and analyzed another nine that looked for a connection between the chemicals and attention deficit hyperactivity disorder. These nine papers don’t provide sufficient proof of a link between exposure to the substances and attention-related problems, says Juleen Lam, an associate research scientist at the University of California-San Francisco and lead author of the paper.

But for flame retardants, which are meant to prevent material from catching on fire, the connection is stark. “The evidence strongly suggests that PBDEs are damaging kids’ intelligence,” Lam says, and thus children should be protected from these substances to “prevent intelligence loss. We’re really seeing this as a wake-up call to policymakers.”

Exactly how PBDEs cause a decline in intelligence is unknown. However, research increasingly suggests they impair the activity of the endocrine system, the body’s delicate system of hormone-producing glands that controls everything from daily sleep-wake cycles to sexual development. And during pregnancy, the endocrine system has an enormous effect on the development of the fetus’s brain.

The paper is a “high-quality study that provides the most robust estimate” of the link between prenatal flame retardant exposure and IQ, says Ami Zota, an environmental health scientist at George Washington University who studies flame retardants but wasn’t involved in the paper.

Several PBDEs—there are many types—have been banned or phased out in the United States. Arlene Blum, a scientist with the Green Science Policy Institute who wasn’t involved in the study, says most new furniture doesn’t contain these flame retardants, as was once the case. But they aren’t going away. A study published in mid-March in the journal Environmental Science & Technology, of which Hurley was the lead author, found that bodily levels of flame retardants have plateaued over time and even increased in certain people. Hurley hypothesizes this is because the flame retardants have made their way into the environment after the materials were thrown away and then incinerated,

Hurley says this is likely because the chemicals are now getting into the food supply, as old furniture and foams containing these chemicals have been thrown into landfills or incinerated, leading flame retardants to leach into runoff or to be spewed into the air.

Bryan Goodman, a spokesman for the American Chemistry Council, an industry group, declined to comment specifically on the study findings, but notes that “flame retardants provide consumers with a critical layer of fire protection, and they help save lives.” He also adds that “the major manufacturers of flame retardants have spent millions of dollars on research both before and after their products go on the market.”

Whether flame retardants like PBDEs make fires less deadly is a point of controversy. Some research suggests they do the opposite, showing that the chemicals can give rise to toxic fumes. Their efficacy, Zota says, is “not really backed up by well-supported data.”

Blum recommends buying new furniture and checking labels (which should say if the material contains flame retardants) to reduce exposure to these chemicals. Regular dusting can also help; PBDEs used to be commonly inserted into foam in furniture, and often become part of household dust. Washing your hands before eating can also help, as chemicals from dust can get onto the hands and into your mouth, Blum says.

“I lost IQ points from lead, and my daughter probably lost them from PBDEs,” Blum says. “It’s time to learn from the [likely effects] of these, and question the use of chemicals that may be harmful.”